It's supposed to take 6-8 weeks... I'm approaching the end of my 7th week of waiting and I still haven't seen anything yet though.
It should turn up eventually. Took 3 months for me, once. Btw, did you post the forms yourself or did the Heathrow people take them away and do it for you? Whenever they took away my forms (no experience with H, but for other companies, e.g. Premier), saying they would post them, most of the time I never got the refunds
